How to create an enamelled cast iron shader in Blender?
Artistic approach using noise and principled bsdf 



I'd use a principled shader along with a specular value of 1 and a roughness value of 0.3 to get the surface appearence of iron. You can break the rules and raise up the clearcoat value to 2 or even higher in order to match the shininess/coating of the reference. For each type of surface bump, you can combine different 3d noises and feed them into the normal socket of a principled shader. I'd also add some color variation to the base color using noise again: